Properties of cementless mortars activated by sodium silicate

Abstract The present paper reports the testing of 12 alkali-activated mortars and a control ordinary portland cement (OPC) mortar. The main aim is to develop cementless binder activated by sodium silicate powder. An alkali quality coefficient combining the amounts of main compositions of source materials and sodium oxide (Na 2 O) in sodium silicate is proposed to assess the properties of alkali activated mortars, based on the hydration mechanism of alkali-activated pastes. Fly ash (FA) and ground granulated blast-furnace slag (GGBS) were employed as source materials. The ratio of Na 2 O-to-source material by weight for different mortars ranged between 0.038 and 0.164; as a result, alkali quality coefficient was varied from 0.0025 to 0.0365. Flow loss of fresh mortar, and shrinkage strain, compressive strength and modulus of rupture of hardened mortars were measured. The compressive strength development of alkali activated mortar was also compared with the design equations for OPC concrete specified in ACI 209 and EC 2. Test results clearly showed that the flow loss and compressive strength development of alkali-activated mortar were significantly dependent on the proposed alkali quality coefficient. In particular, a higher rate of compressive strength development achieved at early age for GGBS-based alkali-activated mortar and at long-term age for FA-based alkali-activated mortar. In addition, shrinkage strain and modulus of rupture of alkali-activated mortar were comparable to those of OPC mortar.

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